The redox properties of some myxoviruses [Fowl plaque virus strain Rostock (FPV), New Castle Disease virus strain Italy (NDV), B/Hong Kong, A/Port Chalmers, A/Victoria, A/Scotland, and A/Fort Dir) and electron microscopic studies as well as by the determination of the hemagglutination (HA) titer (antigen efficiency). The results have shown that viruses decrease the spin concentration of Cu2+ by acting as a reducing species (electron donor) which will result in the inactivation (oxidation) of the virus. Addition of an oxidizing substance, such as H2O2, to a virus suspension also leads to an oxidation of the viruses, and, thus, to their inability to reduce Cu2+. This result is confirmed by the decrease of the HA titer of viruses with increasing Cu2+ concentrations. H2O2 could not be applied for the HA titer test since it interacts with the erythrocytes of the chicken blood used for this determination. Therefore, another oxidizing substance (oxidized glutathione, GSS) was selected which exhibited a slightly less pronounced effect than Cu2+. Since reduced glutathione (GSH) exerts a similar but less pronounced effect than GSS, it might be concluded that viruses have a redox system of their own and act as reducing or oxidizing substance depending on the biological receptor system. Electron microscopic studies confirm this hypothesis. As can be seen by the electron micrographs, increasing concentrations of either Cu2+, GSS, H2O2, KMnO4, or GSH will, finally, result in a complete destruction of the virus. Because of structural similarities it might be assumed that other types of viruses behave very similarly.